Flame retardant blends of polysulfone and polyalkylene phthalate

ABSTRACT

This invention relates to flame retardant blends of polysulfone, with polyalkylene phthalate. The present blends are flame retardant, even at thin part thickness.

BACKGROUND OF THE INVENTION

This invention relates to flame retardant blends of polysulfone, withpolyalkylene phthalate The present blends are flame retardant even atthin part thickness.

Aromatic polymers such as polyethylene terephthalate, polyarylsulfones,and poly(aryl ether) sulfones, in admixture with themselves, or whenblended, do not exhibit adequate flame retardancy. As a result, variousflame retardant additives have been disclosed which render suchcompositions flame retardant in varying degrees of effectiveness.

There are many known flame retardant additives which are employed bymixing them with other materials such as polymers to render materialsflame retardant. Such flame retardant additives have been known to beemployed in amounts of at least 1 weight percent in order to provideflame retardant characteristics to those products which are combustible.

The use of compounds containing phosphorus and/or nitrogen as flameretardant additives for some polymers has been recognized, as has beenthe use of various halogenated materials, such as chlorinated paraffinwax, and antimony compounds such as antimony oxide, and mixturesthereof. One disadvantage, however, in regard to the known materialswhich have been used as flame retardants has been the fact thatgenerally a large amount of the additive must be incorporated into thepolymer to make it sufficiently flame retardant. In addition, flameretardant additives frequently do not stand up to processing conditionsand will in some cases separate out from the resin after incorporation.The search for fire-retarding adjuvants is important because it isessential that many resin compositions have relatively high resistanceto burning if they are to be commercially utilizable. Further, theresins must be capable of enduring heat without deterioration and beable to resist fire and flame. Especially, materials used in conjunctionwith electricity must be able to resist ignition or deterioration byheat and sparks. As the requisite degree of flame retardance isachieved, it is essential that the other desirable qualities of theresinous material be preserved or enhanced. In addition to thepreservation of the mechanical properties of the polymer, it isdesirable that the color should not be adversely affected.

Flame retarding additives such a triphenyl phosphate or aluminumtrihydrate which generally possess low flammability have been mixed withengineering thermoplastics to reduce flammability of the thermoplastics.However, a blend of such a low flammability additive with highperformance engineering thermoplastics often does not yield a useableflame resistant composition. For example, the low flammability additivemay not be compatible, with the engineering thermoplastic, at additiveconcentrations achieving significant flame retardance, resulting inlower levels of flame resistance, or the additive may not be stable atthe processing temperatures of the engineering thermoplastic.Furthermore, low flammability additives which are compatible with aparticular engineering thermoplastic often cannot effectively lower theflammability of the thermoplastic. If the effect on flammability ismerely a reduction due to dilution, then amounts of the low-flammabilityadditive necessary to achieve a desired reduction in flammability canadversely affect the physical properties or processibility of theengineering thermoplastic.

Perfluorocarbon polymers have been used in the past to inhibit drip inthermoplastics and improve heat and smoke release in polysulfone.EPO307,670 to Rock discloses that polysulfone with 10 percentperfluorocarbon added has improved heat and smoke releasecharacteristics. It does not show blends of polyester with polysulfoneor the advantage of adding borate salts to the combination. Further, itdoes not disclose UL-94 test data. EPO400,935 discloses flame retardantglass fiber reinforced polyesters including polyalkylene terephthalateand another polymer. The synergistic flame retardant use of PTFE andborate salts are not taught or suggested. Thermoplastic blends ofaromatic polysulfones and thermoplastic polyesters are known from Nield,U.S. Pat. No. 3,742,087. Nield states that the blends may be mixed withparticles of other polymeric materials as fillers having specialproperties, e.g., elastomeric materials and polytetrafluoroethylene(PTFE). There is no disclosure of the difficulty of achieving flameretardancy (UL-94 at V-1 to V-0) in thin part thickness (e.g. down to 60mils) plastics nor the use of polytetrafluoroethylene in conjunctionwith zinc borate in order to achieve flame retardancy of thin films ofthe present blends. Blends of poly(aryl ether), polyester and acompatibilizing amount of polycarbonate are disclosed in Robeson, U.S.Pat. No. 4,369,136. Robeson discloses that flame retardants may be usedbut does not delineate the particular flame retardants of the presentinvention or the advantages thereof in regard to thin films. In U.S.Ser. No. 753,188 an application by the present inventor, compatibilizedand miscible blends of poly(aryl ether) and/or polycarbonate,polyarylate, and polyester are disclosed. In EPO364,729, a polycarbonatecomposition with PTFE, boric oxide and a graft copolymer of methylmethacrylate, butadiene and styrene and/or styrene-maleic anhydridecopolymer were shown to have a UL-94 of V-0, however polycarbonate withPTFE and boric oxide, without styrene, only achieved a UL-94 of V-1 at1.6 mm.

In Saito, U.S. Pat. No. 4,820,761, polysulfone with PTFE is disclosed asan aid for low mold shrinkage and good mold releasability. There is nomention of the present blends or the use of borate salts.

Zinc borate has been used in various thermoplastic compositions. Cella,et al., U.S. Pat. No. 4,833,190 discloses use of zinc borate as a smokesuppressant and flame retardant in silicone containing compositions.Anderson, U.S. Pat. No. 4,049,619 discloses a thermoplastic compositionof a polysulfone, a flame retarding bisphenoxy compound and an enhancingagent, which is disclosed as including zinc borate.

Anderson, U.S. Pat. Nos. 4,041,013 and 4,049,619 disclose plasticcompositions containing polysulfone and bisphenoxy compounds along withcertain enhancing agents including zinc borate, the preferred enhancingagent being antimony trioxide. There is no teaching of a preference forzinc borate or its synergistic use with PTFE as flame retardants in thepresent thin film blends. In U.S. Pat. No. 4,981,895 to Buchert, amolding composition consisting of polyether sulfone or polyether ketoneor mixtures thereof in conjunction with zinc borate were said to haveimproved heat release characteristics. No mention of the particularpolysulfone of the present invention or its blend with polyester of PTFEwere mentioned. This is significant since blending polyalkylenephthalate with polysulfone while having distinct advantages,significantly reduces flame retardancy of neat polysulfone.

Blends of polysulfone and other polymers such as polyalkylenephthalatecombine the advantageous properties of impact resistance, hydrolyticstability, dimensional stability, and heat resistance of the polysulfoneand yet can be tailored to lower the cost and not interfere with theadvantageous properties. Blends of poly(aryl ether) and polycarbonate orpolyester are known from U.S. Pat. Nos. 3,365,517, 3,742,087, 4,369,136,4,371,672, and 4,746,710. It is shown in these patents that as a resultof the blend the polymers are rendered more resistant to environmentalstress crazing and cracking their heat distortion temperature isincreased and the poly(aryl ether) is made more resistant to thermalstress and aging embrittlement. Furthermore, improved hydrolyticstability is disclosed. Thus, it can be seen that alloying of poly(arylether) sulfone with polyalkylenephthalate leads to materials withimproved physical characteristics.

Unfortunately, by adding polyalkylenephthalate to polysulfone flameretardancy is significantly diminished. Thus, it has become particularlycritical to improve the flame retardancy of the composition, first ofall, in order to bring it up to par with the known flame retardantcompositions utilizing polysulfone in the industry.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is to a blend of polysulfone andpolyalkylenephthalate with optimum flame retarding amounts of a boratesalt and a synergistic amount of polytetrafluoroethylene (PTFE).

It has been found that when polytetrafluoroethylene and zinc boratesalts in the specified proportions are added to blends of the presentpolysulfone and polyester that UL-94 flame retardancy of V-0 can beachieved at part thickness down to 60 mils. A flame retardant polymerblend comprising (a) polysulfone; (b) polyalkylenephthalate; and (c) aflame retardant comprising borate salt and polytetrafluoroethylene.

The polysulfone of the present invention is described in U.S. Pat. Nos.3,264,536, 4,108,837, 4,175,175. It preferably has the followingrepeating units: ##STR1##

The poly(aryl ethers) are prepared by using the alkali metal salt of thedihydric phenols, i.e., the alkali metal carbonate or alkali metalhydroxide process.

If carbonate is used, the polymers are prepared by contactingsubstantially equimolar amounts of the hydroxy-containing compounds andthe dihalo- or dinitrobenzenoid compound, e.g., 4,4'-dichlorodiphenylsulfone or 4,4'-difluorodiphenyl sulfone, with from about 0.5 to about1.0 mole of an alkali metal carbonate per mole of hydroxyl group in asolvent mixture comprising a solvent which forms an azeotrope with waterin order to maintain the reaction medium at substantially anhydrousconditions during the polymerization.

The temperature of the reaction mixture is kept at about 170° C. toabout 250° C., preferably from about 210° C. to about 235° C. for aboutone to about 15 hours. However, lower or higher temperatures may also beadequate.

In a modification which is particularly suitable for making copolymersfrom bisphenol A and one or more additional dihydroxy compounds, thereactants other than said additional dihydroxy compounds are charged andheated at from about 120° C. to about 180° C. for about 1 to about 5hours, said additional dihydroxy compounds are added, the temperature israised and the mixture is heated at from about 200° C. to about 250° C.,preferably from about 210° C. to about 240° C., for about one to 10hours. This modification is further described in D. R. Kelsey, et al.,U.S. Pat. No. 4,783,520, hereby incorporated by reference.

The reaction is carried out in an inert atmosphere, e.g., nitrogen, atatmospheric pressure, although higher or lower pressures may also beused.

The poly(aryl ether) is then recovered by conventional techniques suchas coagulation, solvent evaporation, and the like.

The solvent mixture comprises a solvent which forms an azeotrope withwater and a polar aprotic solvent. The solvent which forms an azeotropewith water includes an aromatic hydrocarbon such as benzene, toluene,xylene, ethylbenzene, chlorobenzene, and the like.

The polar aprotic solvents employed in this invention are thosegenerally known in the art for the manufacture of poly(aryl ether)sulfones and include sulfur-containing solvents such as those of theformula:

    R.sub.4 --S(O)δ--R.sub.4

in which each R₄ represents a monovalent lower hydrocarbon group free ofaliphatic unsaturation, which preferably contains less than about 8carbon atoms or when connected together represent a divalent alkylenegroup with δ being an integer from 1 to 2 inclusive. Thus, in all ofthese solvents, all oxygens and 2 carbon atoms are bonded to the sulfuratom. Contemplated for use in this invention are such solvents as thosehaving the formula: ##STR2## where the R₅ groups are independently loweralkyl, such as methyl, ethyl, propyl, butyl, and like groups, and arylgroups such as phenyl and alkylphenyl groups such as the tolyl group, aswell as those where the R₅ groups are interconnected as in a divalentalkylene bridge such as: ##STR3## in tetrahydrothiophene oxides anddioxides. Specifically, these solvents include dimethylsulfoxide,dimethylsulfone, diphenylsulfone, diethylsulfoxide, diethylsulfone,diisopropylsulfone, tetrahydrothiophene 1,1-dioxide (commonly calledtetramethylene sulfone or sulfolane) and tetrahydrothiophene-1 monoxide.

Additionally, nitrogen-containing solvents may be used. These includedimethylacetamide, dimethylformamide and N-methylpyrrolidone.

The azeotrope-forming solvent and polar aprotic solvent are used in aweight ratio of from about 1:10 to about 1:1, preferably from 1:5 toabout 1:3.

In reaction, the hydroxy-containing compound is slowly converted, insitu, to the alkali salt thereof by reacting with the alkali metalcarbonate. The alkali metal carbonate is preferably potassium carbonate.As indicated before, mixtures of carbonates such as potassium and sodiumcarbonate may also be used.

Water is continuously removed from the reaction mass as an azeotropewith the azeotrope-forming solvent so that substantially anhydrousconditions are maintained during the polymerization.

It is essential that the reaction medium be maintained substantiallyanhydrous during the polycondensation. While amounts of water up toabout 1 percent can be tolerated, and are somewhat beneficial whenemployed with fluorinated dihalobenzenoid compounds, amounts of watersubstantially greater than this are desirably avoided as the reaction ofwater with the halo and/or nitro compound leads to formation of phenolicspecies and only low molecular weight products are secured.Consequently, in order to secure the high polymers, the system should besubstantially anhydrous, and preferably contain less than 0.5 percent byweight water during the reaction.

When using alkali metal, an alkali metal salt of a dihydric phenol iscontacted with a dihalobenzenoid compound in the presence of asulfur-containing solvent as herein above defined under substantiallyanhydrous conditions.

Additionally, the poly(aryl ethers) may be prepared by other methodsknown in the prior art, in which at least 1 dihydric phenol and at least1 dihalobenzenoid compound are heated, for example, with a mixture ofsodium carbonate or bicarbonate and a second alkali metal carbonate orbicarbonate having a higher atomic number than that of sodium, asdescribed in U.S. Pat. No. 4,176,222. Bulk processes are also known.

The poly(aryl ethers) have reduced viscosities in the range of fromabout 0.35 to about 1.2 dl/g, preferably from about 0.38 to about 1.0dl/g, as measured in chloroform or another appropriate solvent, at 25°C. or at another appropriate temperature, at a concentration of 0.2g/100 ml. At reduced viscosities below about 0.35 dl/g, the poly(arylethers) are brittle; at reduced viscosities higher than about 1.2 dl/g,the poly(aryl ethers) have very high melt viscosities and are verydifficult to fabricate from the melt.

The weight percent of polysulfone used in compositions of the inventionis in the range of about 20 parts to about 80 percent of polymericmaterial.

The most preferred polysulfone is a poly(aryl ether) including repeatingmoieties as shown: ##STR4## It is available commercially from AmocoPerformance Products, Inc. under the trade name Udel® P-3703. It has areduced viscosity of about 0.43 dl/g as measured in chloroform at aconcentration of 0.2 g/dl and 25° C. It has a number-average molecularweight of about 13,000 as measured by gel permeation chromatography(GPC) using tetrahydrofuran (THF) as solvent and polystyrene calibrationstandards.

Polyalkylene Phthalates

The polyesters which are suitable for use herein are derived from analiphatic or cycloaliphatic diol, or mixtures thereof, containing from 2to about 10 carbon atoms and at least 1 aromatic dicarboxylic acid. Thepolyesters which are derived from an aliphatic diol and an aromaticdicarboxylic acid have repeating units of the following general formula:##STR5## wherein x is an integer of from 2 to 4.

The preferred polyesters are poly(ethylene terephthalate) andpoly(butylene terephthalate).

Also contemplated herein are the above polyesters with minor amounts,e.g., from 0.5 to about 2 percent by weight, of units derived fromaliphatic acid and/or aliphatic polyols, to form copolyesters. Thealiphatic polyols include glycols, such as poly(ethylene glycol). Thesecan be made following the teachings of, for example, U.S. Pat. Nos.2,465,319 and 3,047,539.

The polyesters which are derived from a cycloaliphatic diol and anaromatic dicarboxylic acid are prepared by condensing either the cis- ortrans-isomer (or mixtures thereof) of, for example,1,4-cyclohexanedimethanol with an aromatic dicarboxylic acid so as toproduce a polyester having recurring units of the following formula:##STR6## wherein the cyclohexane ring is selected from the cis- andtrans-isomer thereof and R₆ represents an aryl radical containing 6 to20 carbon atoms and which is the decarboxylated residue derived from anaromatic dicarboxylic acid.

Examples of aromatic dicarboxylic acids indicated by R₆ in formula (26),are isophthalic or terephthalic acid, 1,2-di(p-carboxyphenyl)ethane,4,4'-dicarboxydiphenyl ether, etc., and mixtures of these. All of theseacids contain at least 1 aromatic nucleus. Fused rings can also bepresent, such as in 1,4-or 1,5-naphthalenedicarboxylic acids. Thepreferred dicarboxylic acids are terephthalic acid or a mixture ofterephthalic and isophthalic acids.

A preferred polyester may be derived from the reaction of either thecis-or trans-isomer (or a mixture thereof) of 1,4-cyclohexanedimethanolwith a mixture of isophthalic and terephthalic acids. The polyestershave repeating units of the formula: ##STR7##

Another preferred polyester is a copolyester derived from a cyclohexanedimethanol, an alkylene glycol and an aromatic dicarboxylic acid. Thesecopolyesters are prepared by condensing either the cis-or trans-isomer(or mixtures thereof) of, for example, 1,4-cyclohexanedimethanol and analkylene glycol with an aromatic dicarboxylic acid so as to produce acopolyester having repeating units of the following formula: ##STR8##wherein the cyclohexane ring is selected from the cis- and trans-isomersthereof, R₆ is as previously defined, x is an integer of 2 to 4, the y¹units comprise from about 10 to about 90 mole percent and the y¹ unitscomprise from about 10 to about 90 mole percent of the total (y+y¹)units.

The preferred copolyester may be derived from the reaction of either thecis- or trans-isomer (or mixtures thereof) of 1,4-cyclohexanedimethanoland ethylene glycol with terephthalic acid in a molar ratio of 1:2:3.These copolyesters have repeating units of the following formula:##STR9## wherein y and y¹ are as previously defined.

The polyesters as described herein are either commercially available orcan be produced by methods well-known in the art, such as those setforth in, for example, U.S. Pat. No. 2,901,466.

The polyesters used herein have an intrinsic viscosity of from about 0.4to about 2.0 dl/g as measured in a 60:40 phenol/tetrachloroethanemixture or similar solvent at 23°-30° C.

Borate Salts

The borate used should be anhydrous, having water amounts less than 0.2weight percent of the borate; hydrated borate or borates with greaterwater content can result in unprocessable compositions. Any suitableanhydrous zinc borate may be used. Anhydrous zinc borate having aparticle size of 6-10 microns, is available as XPI-187 from U.S. Boraxand is produced by thermal dehydration of zinc borate at 500° C. Theamount of zinc borate to be used is an effective amount to achieve flameretardance, and preferably is about 1.0 to about 10.0 parts by weightper 100 parts combined weight of the total composition.

Polytetrafluoroethylene (PTFE)

PTFE can be purchased from Du Pont or Ausimont.

Paste:

This is a high molecular weight form of PTFE that is prepared as adispersion of about 0.2 microns. This material is then coagulated togive particles of about 400 to 500 microns. These materials are soft andfibrillate at room temperature. Typical grades of this type are:Algoflon DF 1, DF 200 and DFC.

Granular:

This is a high molecular weight PTFE that is made in a suspensionprocess that results in a 20 micron size powder. This materialfibrillates at high temperature or under high sheer conditions. Typicalgrades are: Algoflon F5, F2 and F6.

Wax:

This is a low molecular weight PTFE that has no tendency to fibrillate.This material is usually made by degrading high molecular weightmaterials using radiation. The particle size varies by grade and istypically 6 to 25 microns. This type can be formed from direct reactionfrom the monomer, but that is not the process that Ausimont uses.Typical grades are: Polymist F-5A, F-5, and F-510.

Teflon T-60 is a fibrillating fluoropolymer supplied by EI Du PontDeNemours Inc.

Preparation of Blends

In preparing the blends of the present invention the individualcomponents are commonly provided in the form of chips, pellets orpowders, and physically mixed together in any appropriate apparatus,e.g., a mechanical drum tumbler. The physical mixture can be then driedif desired, preferably under vacuum or in a circulating air oven,although any other suitable apparatus can be used. The purpose of thedrying step is to remove water from the physical mixture so as toprevent degradation. After the mixture of the solid polymer particles(which, optionally, may also contain reinforcing filler, fiber, and thelike-vide infra) has been dried, the blend can be prepared. A convenientmethod of forming the blend is melt extrusion. The extrusion apparatusthoroughly mixes the polymers in the melt and then extrudes the blend inthe form of a strand which, upon solidification, can be broken up intochips or pellets. Both single screw and twin-screw extruders can be usedfor the preparation of the instant blends.

Any suitable procedure can be used to compound the compositions of theinvention, and the solid components can be mixed with each other in anyparticular order. Applicants prefer to blend desirable amounts of allsolids present and then heat the resulting mixture to above thetransition temperature (Tg) of the highest Tg polymer in the mixture.The molten mixture is then mixed for any suitable period to achievethorough dispersion of the additive(s) and mixing of the polymerspresent, and then extruded and cooled into any desirable shape. Such aprocess can be conveniently carried out with commercial extruders suchas a Berstorff. In the compositions of the invention which comprisesTiO₂, it is not necessary to add the oxide initially. For example, thecomposition containing zinc borate can be compounded first, anddesirable amounts of TiO₂ can be mixed in later.

All materials were prepared by first dry blending the components using amechanical blender (turned end over end). They were then compoundedusing a Berstorff ZE25, 25 mm corotating twin-screw extruder.

The resulting mixture is then fed to an extruder operating at about 265°C., and the extrudate is formed into pellets. These pellets are theninjection molded at about 300° C. into test bars of about 5 inches by1/2 inch by about 1/16 inch thick. Five test bars are subject to thetest procedure set forth in Underwriters' Laboratories Inc., SubjectUL-94, Burning Test for Classifying Materials. In accordance with thistest procedure, materials so investigated are rated either V-0, V-1, orV-2 based on the results of 5 specimens. The criteria for each ratingper UL-94 is shown under experimental methods.

The instant alloys can be melt processed in the substantial absence ofpolymer degradation to form a variety of relatively stiff shapedarticles, e.g., molded three-dimensional articles, fibers, films, tapes,etc.

Articles may also be molded from a molding compound which includes, as 1component, the blend of the present invention. Such a molding compoundincorporates into the blend of the present invention approximately 1 to50 percent, preferably approximately 10 to 30 percent by weight, basedupon the total weight of the molding compound, of a solid filler and/orreinforcing agent. Representative fibers which may serve as reinforcingmedia include glass fibers, asbestos, graphitic carbon fibers, amorphouscarbon fibers, synthetic polymeric fibers, aluminum fibers, aluminumsilicate fibers, oxide of aluminum fibers, titanium fibers, magnesiumfibers, wollastonite, rock wool fibers, steel fibers, tungsten fibers,cotton, wool, and wood cellulose fibers, etc. Representative fillermaterials include glass, calcium silicate, silica, clays, talc, mica,carbon black, titanium dioxide, wollastonite, polytetrafluoroethylene,graphite, alumina trihydrate, sodium aluminum carbonate, barium ferrite,etc.

The polymers may also include additives such as thermal stabilizers,ultraviolet light stabilizers, plasticizers, and the like.

The materials of this invention may be fabricated into any desiredshape, i.e. moldings, coatings, films or fibers.

EXPERIMENTAL

The following designations are used throughout to describe the polymersreferred to in the examples:

Polysulfone-A poly(aryl ether) having the repeat unit of formula:##STR10## It is available commercially from Amoco Performance Products,Inc. under the trade name Udel® P-3703. It has a reduced viscosity ofabout 0.43 dl/g as measured in chloroform at a concentration of 0.2 g/dland 25° C. It has a number-average molecular weight of about 13,000 asmeasured by gel permeation chromatography (GPC) using tetrahydrofuran(THF) as solvent and polystyrene calibration standards.

Another polysulfone that may be used includes the following repeatingunit. One such polysulfone is available commercially from ImperialChemical Incorporated: ##STR11##

PET:

Poly(ethylene terephthalate)--A polymer having the following repeat unitstructure: ##STR12##

This polymer is widely available from a number of U.S. suppliers. Theresin used carried the trade name Cleartuff 7202 and is a product ofGoodyear Co. This material has a Tg of about 80° C. in the fullyamorphous state (the Tg increases slightly with the level ofcrystallinity). The polymer has a crystalline melting point of about260° C. as measured by differential scanning calorimetry.

ZnO is zinc oxide, an inorganic filler that when reacted with boric acidis able to produce zinc borate. It was used in powder form.

OCF (Owens Corning Fiberglass) 497-DB is 1/2" long chopped glass with anappropriate sizing agent for compatibility with the polymer matrix.

Kemamide W-405 N,N'-ethylenebisstearamide, fatty bisamide derived fromstearic acid (sold by Humko Chemical).

KZTPP is a cyclo[dineopentyl(diallyl)]pyrophosphatedineopentyl(diallyl)zirconate chemical structure is shown below.##STR13## It is manufactured by Kenrich Petrochemicals, Inc. of Bayonne,N.J.

Experimental Methods

Specimens obtained from the experiments embodied in the examples belowwere tested by a variety of techniques using standard 5"×0.5"×0.125"injection molded specimens (ASTM D-790). Instrumented impactmeasurements we performed on 0.125 inch thick circular disk injectionmoldings 2 inch in diameter.

Failure Load is determined using a instrument impact tester such as thatmanufactured by Dynatup. The failure load is determined by measuring theforce at peak-energy absorbed by a molded part by a falling tup prior tocrack propagation.

Max. load is determine using the same instrument as described above.This value is determined by measuring the force at total energy absorbedby a molded part by a falling tup.

Sp Gr is measured on molded parts to determine its density relative towater.

Flex Str. is a mechanical property test performed according to ASTMD-790. Flammability testing was performed per the UL-94 vertical burntest specifications using ASTM injection molding 5"×0.5"×0.62" nominaldimensions.

Flammability Ratings

"94 V-0":

No single flaming combustion after removal of the igniting flame shallexceed 10 seconds and none of the specimens shall drip flaming particleswhich ignite absorbent surgical cotton placed 12" below the specimen.Total flame out time for all 5 specimens (10 ignitions) cannot exceed 50seconds.

"94 V-1":

No single flaming combustion after removal of the igniting flame shallexceed 30 seconds and none of the specimens shall drip flaming particleswhich ignite absorbent surgical cotton placed 12" below the specimen.Total flame out time for all 5 specimens (10 ignitions) cannot exceed250 seconds.

"94 V-2":

No single flaming combustion after removal of the igniting flame shallexceed 30 seconds. The specimens drip flaming particles which burn onlybriefly, some of which ignite absorbent surgical cotton placed 12" belowthe specimen. Total flame out time for all 5 specimens (10 ignitions)cannot exceed 250 seconds.

In addition, a test bar which continues to burn for more than 30 secondsafter removal of the igniting flame is classified, not by UL-94, but bythe standards of the instant invention, as "burns." Further, UL-94requires that all test bars in each test group must meet the V typerating to achieve the particular classification. Otherwise, the 5 barsreceive the rating of the worst single bar. For example, if 1 bar isclassified as 94 V-2 and the other 4 are classified as 94 V-0, then therating for all 5 bars is 94 V-2.

EXAMPLES

The following examples are intended to give specific illustrations ofthe practice of this invention and are not intended in any way to limitthe scope of this invention.

Comparative Example 1(C-1)

A 75/25 by weight blend of UDEL P-3703 polysulfone (PSF-3703) andCleartuff® 7207 poly(ethylene terephthalate) (PET) were tumble-mixed anddried as described in Comparative Example 1. The dry pellet mix was thenmelt-blended using the equipment described in Comparative Example 1. Thesame conditions were used except for a lower melt temperature of about290° C. The blend was dried and molded as described in ComparativeExample 1, except for lower processing temperatures. The barreltemperature profile used was 270°-295° C. with a nozzle temperature of295° C. The mold temperature was set at 90° C. The molded 0.062" thickspecimens were tested for flammability in accordance with the UL-94vertical burn specification. The results from this test, which are givenin Table 1, indicated that this blend does not meet any of the UL-94classifications for flammability resistance. That was because the burntimes were exceeded for both the maximum burn time for a singleapplication as well as for the cumulative burn time for the 5 specimenstested.

Comparative Example 2(C-2)

A 65/35 by weight blend of the same PSF and PET resins used inComparative Example 2 was prepared by first drying the resins as perComparative Examples 1, and then extruding the dry mix through anon-vented twin screw Brabender counter-rotating twin-screw unit. Theblend was run through the extruder at a rate of 4.5 lb/hr and the melttemperature was about 290° C. The screw speed of extruder was 40 rpm.The blend sample thus produced was dried again prior to injectionmolding into 0.062"-thick specimens using the Arburg injection moldingmachine and conditions described in Comparative Example 2. UL-94flammability testing was performed on specimens from this polymer blendand the results are summarized in Table 1. The specimens from thissample burned vigorously on the first flame application which did notstop to allow a second flame application. Additionally, 4 out of 5specimens dripped igniting cotton on the floor of the test chamber. Thismaterial thus failed the UL-94 vertical flammability test in all itsclassifications.

Example 1

The following blend composition was prepared using weight percentages ofthe various components as indicated: Udel P-3703 (68.63%), PET (22.87%),zinc borate (6%), and F5A non-fibrillating PTFE (2.5%). The blend wasprepared and tested following procedures substantially similar to thosedescribed in Comparative Example 2. The UL-94 flammability resultsobtained for this composition show a marked improvement in flammabilityover the corresponding control case embodied in Example 2. Theflammability rating based on the burning behavior and durations was V-1.The burn times are given in Table 1. The synergistic effect of PTFE andzinc borate is thus demonstrated.

Example 2

The following blend composition was prepared using weight percentages ofthe various components as indicated: Udel P-3703 (65.25%), PET (21.75,),zinc borate (9%), and F5A non-fibrillating PTFE (4%). The blend wasprepared and tested following procedures substantially similar to thosedescribed in Comparative Example 2. The UL-94 flammability resultsobtained for this composition show a marked improvement in flammabilityover the corresponding control case embodied in Example 2. Comparingwith Example 2, there is also a significant benefit obtained fromincreasing the level of the two flame retardants in the composition. Theflammability rating of this formulation based on the burning behaviorand durations was V-1. The key burn times are given in Table 1.

EXAMPLES 3-5

Three PSF/PET flame retarded blend compositions were prepared from Udel®P-3703 PSF, PET, zinc borate, and Algoflon DM-1, another fibrillatingPTFE supplied by Du Pont. For each of the three formulations the ratioof PSF to PET was maintained at 65/35 by weight. All three formulationscontained 6 weight percent zinc borate and the level of DM-1 was 1, 2,and 3 weight percent, respectively, for the three formulations. Theexact weight percentages of the four components are given in Table 3.These materials were prepared, molded into 0.062"-thick ASTM bars andtested for flammability behavior using very similar procedures to thoseemployed in Example 2. The UL-94 flammability rating for theseformulations was V-1 for all three cases, and the burn times decreasedfor the three formulations, as shown in Table 3, in a manner consistentwith the level of DM-1 fluoropolymer.

Other compositions were prepared by the same method as Examples 1-5 thecompositions and results are shown in Table I.

Examples 6 and 7

Two more formulations were prepared similar to those of Examples 3-5above, except that the level of DM-1 was maintained at 2 weight percentwhile the level of zinc borate was lowered to 4 and 2 weight percent,respectively, the exact compositions are, again, given in Table 1 alongwith the UL-94 flammability results. While both of these formulationsafforded a V-1 flammability rating, the composition containing 4 weightpercent zinc borate gave significantly better performance than thatcontaining only 2 percent zinc borate. This supports the notion that asynergistic effect exists in this dual flame retardant system. Thissynergism is apparently lost if the ratio of zinc borate of PTFE iseither too high or too low.

Example 8 and Comparative Example 3 (C-3)

To investigate the effect of PSF/PET ratio on the flammabilityperformance of these formulations, two additional compositions wereprepared in which this ratio was set at 75/25 and 55/45, while thelevels of DM-1 PTFE and zinc borate were maintained at 2 and 6 weightpercent for both compositions. The pertinent data for these two examplesare given in Table 1. The UL-94 result for the first formulation is V-1with a relatively low cumulative burn time of about 90 seconds. For thesecond formulation (55/45 PSF/PET ratio), on the other hand, noacceptable vertical flammability rating is achieved with the total burnwell exceeding the 250 sec limit required for V-2. It is thus noted thatthe UL-94 flammability performance is sensitive to the PSF/PET ratio.For ratios significantly lower than 60/40 PSF/PET it is unlikely thatthe flame retardance additives of this invention will be effective.

                                      TABLE 1                                     __________________________________________________________________________                Example No.                                                                   D  E      F  G   H  I  J C-1    1   2  C-2    3                   __________________________________________________________________________    PSF Udel P1700 (wt %)                                                                     97 95     93 97.5                                                                              95                                               PSF P3703                              75   68.63                                                                             65.25                                                                            65     60.45               PC Lexan 104                                                                  PC Lexan 2015                                                                 PET Cleartuf                           25   22.87                                                                             21.75                                                                            35     32.55               Makrolon 3108                                                                 ZnBO.sub.3 Ground                                                             ZnBO.sub.3   3  5      7                    6   9         6                   Boric Acid                                                                    PTFE F5A                 2.5 5              2.5 4                             DF-1 Algoflon                                             1                   T-60                                                                          ZnO                                                                           OCF 497 DB                                                                    Kemamide W40                                                                  Ultracarb                                                                     Antimony Oxide                                                                KZTPP                                                                         Decabromo FR                                                                  Total Burn (sec)                                                                          60 79     37 22  24.5    >250   111 66 384    170.3               Highest Single Burn                                                                       23 32      8 5   4        >60   30  14 >75    27                  Rating (UL-94)                                                                            V-2                                                                              Greater than                                                                         V-0                                                                              V-0 V-0     Greater than                                                                         V-1 V-1                                                                              Greater                                                                              V-1n                               V-2                   V-2           V-2                        Failure load (lbs)                                                            Max. load (lbs)                                                               Sp Gr                                                                         Flex Strength (psi)                                                           __________________________________________________________________________                                   Example No.                                                                   4   5   K   L   M  N      O  P                 __________________________________________________________________________                       PSF Udel P1700 (wt %)                                                         PSF P3703   59.80                                                                             59.15                                                                             61.10                                                                             62.40                                                                             69 50.6   41 41                                   PC Lexan 104                                                                  PC Lexan 2015                                                                 PET Cleartuf                                                                              32.20                                                                             31.85                                                                             32.90                                                                             33.60                                                                             23 41.4   23 22.5                                 Makrolon 3108                         7.0                                                                              6.0                                  ZnBO.sub.3 Ground                                                             ZnBO.sub.3  6   6   4   2   6  6         6                                    Boric Acid                                                                    PTFE F5A                                 2.5                                  DF-1 Algoflon                                                                             2   3   2   2   2  2                                              T-60                                                                          ZnO                                                                           OCF 497 DB                            22 21                                   Kemamide W40                          1.0                                                                              1.0                                  Ultracarb                                                                     Antimony Oxide                                                                KZTPP                                                                         Decabromo FR                          6.0                                     Total Burn (sec)                                                                          150.6                                                                             129.6                                                                             128.2                                                                             168.3                                                                             91.3                                                                             464.7                                          Highest Single Burn                                                                       27  21  22  27  17 123                                            Rating (UL-94)                                                                            V-1 V-1 V-1 V-1 V-1                                                                              Greater                                                                              V-0n                                                                             V-2                                                                 V-2                                            Failure load (lbs)                                                            Max. load (lbs)                                                               Sp Gr                                                                         Flex Strength (psi)                                        __________________________________________________________________________

That which is claimed is:
 1. A flame retardant polymer blend comprising (a) polysulfone; (b) polyalkylenephthalate; (c) borate salt; and (d) polytetrafluoroethylene.
 2. The flame retardant blend of claim 1 consisting essentially of polysulfone, polyalkylenephthalate, polytetrafluoroethylene and zinc borate.
 3. The flame retardant blend of claim 1 consisting essentially of a weight ratio of polysulfone to polyalkylene phthalate of 95:5 to 50:50.
 4. The flame retardant blend of claim 1 consisting essentially of a ratio of polysulfone to polyalkylenephthalate of about 60:40.
 5. The flame retardant blend of claim 1 wherein said polytetrafluoroethylene is present in the amount of 0.5 to 10 weight percent.
 6. The flame retardant blend of claim 1 wherein the borate salt is zinc borate present in an amount of 1 to 10 weight percent.
 7. The blend of claim 1 wherein the polysulfone comprises the following repeat unit: ##STR14##
 8. The blend of claim 1 wherein the polysulfone comprises the following repeat unit: ##STR15##
 9. Blend of claim 1 wherein said polyalkylene phthalate comprises the following repeating unit: ##STR16##
 10. The blend of claim 1 wherein the polysulfone consists essentially of the following repeat unit: ##STR17## 